The accurate metering of low fuel flows (of the order of a few pounds per hour) may be attained only with great difficulty. To meter low flows small metering areas are mandated, notwithstanding the provision of a metering head or pressure differential across the metering valve of minimal value. Metering valves adapted to provide small metering areas do not readily lend themselves to easy manufacture and are susceptible to clogging. Moreover, at low fuel flows, the discharge coefficient of the metering area tends to vary with fuel temperature to a greater extent than it would at higher flows.
Certain fuel metering systems in automobiles employ pulsed solenoids in order to interrupt the flow to the engine in such a manner as to produce a desired flow rate. However, flow stoppages of this nature engender pressure spike fluctuations which affect the proper functioning of upstream flow control elements.